Thermoplastics have been used for some time as constituents of household devices. The thermoplastics here are frequently used as worktops or as functional parts or housing parts.
For example, DE-A 19604370 discloses worktops made from thermoplastics comprising a sheet of plastic, to the underside of which has been applied a support apparatus composed of a grid-like component with an open lower side.
DE-A 1 97 22 339 discloses a layered composite material which comprises a support layer made from polypropylene, a decorative layer arranged thereupon, and a heat-cured layer applied to the decorative layer, DE-A 19 858 173 moreover describes a layered composite material made from a support layer of various other thermoplastic polymers, for example made from certain copolymers of styrene or from polyoxymethylene or, respectively, from polybutylene terephthalate, together with a decorative layer applied thereto and a heat-cured layer located on the decorative layer. Compared with conventional layered composite materials with support layers made from wood, from wood fibers or from paper, layered composite materials of this type made from a support layer made from thermoplastic polymers have, inter alia, high temperature resistance and high moisture resistance, and better mechanical strength, and are easier to process.
It is also known that drum-shaped inner containers of household devices can be produced from thermoplastic polymers, mostly from reinforced polypropylene. Inner containers of this type are composed of only one wall, which for reasons of strength has ribs or offset walling elements. A disadvantage of these structures is that this design sometimes requires expensive plastics and/or high wall thicknesses in order to accept the loadings which arise. There are even some desirable versions of devices (with very high spin speeds) which cannot be produced industrially by the lower-cost method of production using plastics. A disadvantage of high wall thicknesses is the need to accept very long solidification times in injection molding, as well as high materials consumption, and this also increases the cost of producing the parts. The reason for this lies in the way the components have to be designed. An important criterion for an inner container is the stiffness of its wall to which the bearing is introduced or applied. In simple terms, the washing and spinning procedures of the household device, for example of the washing machine, together with the unbalanced mass (laundry) in the inner drum, subject the rear wall of the device to a variable flexural load resulting from the tumbling action of the inner drum in the holding vessel. However, this tumbling is permissible only to the extent that the inner drum does not touch the holding vessel. This consideration also applies to the inner drum in washing or drying devices which are currently still produced from sheet steel with reinforcement by diecast metal. Here, too, the stiffness of the shaped part, in particular the stiffness of the drum axle and of the rear wall of the drum are necessary in order to dissipate the force exerted by the unbalanced mass, while not generating excessive deformation.
Drum-shaped inner containers produced from thermoplastics and used in household devices have hitherto been suitable only for application sectors with limited mechanical loading. This implies, inter alia, that the spin rotation rate and the unbalanced mass for drum-shaped inner containers of this type should not be too great. The limited load-bearing capability of the drums made from thermoplastics known hitherto has also limited the number of thermoplastic materials which can be used.
It is an object of the present invention, therefore, to remove the disadvantages described and to provide an improved drum-shaped inner container for household devices, made from thermoplastics and capable of operation even at increased spin rotation rates and/or with an increased unbalanced mass. It should be possible to produce the drum-shaped inner container from a very wide variety of thermoplastics, and the drum should moreover also have very low overall depth.